This invention relates to roller bearing devices of elegant simplicity wherein endless circulating cylindrical rollers are interposed between two members to facilitate relative motion therebetween and in combination with certain apparatus where they have found good utility. More specifically it relates to what is sometimes called a parallel roller type device wherein a plurality of rollers are located in and fill an endless groove, are generally aligned each with the next adjacent roller, and roll in the same general direction. In the preferred approach, they are characterized as having the diameter (end faces) and length of differing size, although in this connection the diameter may be either larger or smaller than the length of the roller.
Heretofore in bearing devices where infinite rectilinear motion between two members is a desired use, cross axis rollers and parallel rollers have been used. Cross axis rollers accept loads between two members from every direction, however at the expense of generally having only one half of the members working to carry the load at any point in time, complexity in manufacture of the groove and/or retention of rollers therein, difficulty at the transition from bearing to non bearing relationship, limitation on the practical number of rollers that can be used, and a variety of other problems which are partially explicated in issued U.S. Pat. No. 4,688,950 invented by Yasunori Yokota, assigned to Nippon Thompson Co., dated Aug. 25, 1987 and U.S. Pat. No. 4,511,189 of Tatsuo Mottate, dated Apr. 16, 1985 assigned to the same assignee.
On the other hand, so called parallel roller devices having endless circulation passages and which may be burdened from every direction are by conventional wisdom conceived of as necessitating at least four rows of endless circulation passages, (one to receive a load from each of the four load quadrants toward the center). (See e.g. Col. 1 of U.S. Pat. No. 4,735,514 of Namomi Kasai dated Apr. 5, 1988, also assigned to Nippon Thompson Co.) The conventional wisdom further concludes that such parallel construction has the necessary defects of large height and width per bearing per unit load capabilities or much complication is involved (with consequent tolerance build up) or both.
Another aspect of prior art problems is the obtainment of a relatively high degree of precision in roller bearings with moderate cost. The precision of the end product is a function of the inherent tolerances involved in the various potential methods of manufacture, tolerance build up occasioned by assembly of components, and types of material employed. Generally in the prior art, obtainment of precision is possible at great cost. As a generalism however, the less parts employed, the less total tolerance build up encountered.
Also in the prior art, the providing of a four quadrant mechanism to handle all direction burden often adds unnecessary cost. That obtains in those devices where the use does not require that the burdens encountered on the bearing device be uniform--i.e. it is quite common that burdens on the device will be larger and of substantially larger duration in two of the four quadrants with the opposite two quadrants receiving relatively lighter burdens which are often transitory. Thus the expense of providing the usual mirror image type capability of four quadrant loading is often needlessly high, since the precision and load capabilities in two quadrants exceeds field requirements.
Another prior art problem is the location of the bearing in potentially dirty environments where occasional debris is encountered which may be capable of expensive damage to both of the relatively moving members (track and car) and the rollers. With respect to comparative costs between the members and the rollers, it will be appreciated that the track and car members are more expensive and damage to either of these car or track members causes considerably more expense to replace compared to the much less costly rollers.
Another prior art problem has been the inability to provide relatively good corrosion resistance to parallel roller bearing structures at reasonable cost while maintaining a relatively high degree of precision.
Another problem in the prior art devices is the complexity which is caused by numerous components. This gives deleterious resultant cost of inventory where mass manufacturing is employed and a higher cost of assembly. Field problems will also be encountered in complex assemblies which have junctions of parts in the wear path because of both potential non uniform wear, and/or minute mating of parts at their coterminus junctions.
Still another problem in the prior art is a failure to fully utilize the relatively low cost versatility of and complexity of shapes available in precision extrusions. For example internal chambers may be used for operations to effectuate relative movement of the two members separated by the bearings. Also, there is a failure to exploit the quite good geometric precision and spaced precision relationships in a variety of load bearing surfaces along the length of members without machining of the surfaces.
In sailboats and other similar apparatus which are exposed to weather and/or where humans come into intimate contact with the apparatus, prior art parallel roller devices do not simultaneously meet the desired attributes of simplicity, ease of maintenance and/or replacement, a construction which will resist trapping debris and providing a minimum of surfaces or crannies to collect unwanted dirt, and is easy to install. It will also be appreciated that the prior art devices are not constructed so as to be relatively hard to freeze up when encountering below freezing temperatures (lacks self draining construction). Also the prior art constructions do not carry high shock loads with ease at low cost, while accommodating to and operational in environments with all directional burdening.
Another prior art problem has been the relatively high cost of parallel roller bearing devices for relative rectilinear movement of members which has, from a practical standpoint, precluded their use in construction of a larger apparatus where reasonably high precision movement is needed (e.g. as in X Y Z movement apparatus used for mixing/dispensing/ratioing/pumping (or any one or combination) of work fluid(s) for precision deposition (batch or continuous). See for example copending application of John O. Roeser for METHOD AND APPARATUS FOR PRECISION PUMPING, RATIOING AND DISPENSING OF WORK FLUID(S) Ser. No. 07/118,330, filed Nov. 6, 1987 and assigned to Otto Engineering, Inc. In such devices Thompson rods and associated bearings were used to give reasonably high rectilinear movement precision commensurate with other components in the system at a reasonable and competitive cost (e.g. precision of movement in the range of 0.01 to 0.00001 inches or higher).
In prior art X Y Z devices, the weight and bulk of parallel roller type bearing devices has been dimensional with the consequent effects thereof. Also, such large mass, which must be moved in each of the planes, caused increased cost of power sources for movement, more support structures and had other deleterious effects. High mass and bulk of prior art parallel rollers could preclude practical use in association with certain desirable high precision but low power operators (such as linear magnetic motors), where they may be otherwise desired.
A search was conducted on the subject matter herein and the following references were developed:
______________________________________ DATE U.S. PAT. NO. INVENTOR/ASSIGNEE ______________________________________ 4/5/88 4,735,514 Kasai/Nippon Thompson Co. Ltd. 12/29/87 4,715,729 Tanaka/Nippon Thompson Co. Ltd. 10/27/87 4,702,622 Teramachi 9/8/87 4,692,037 Kasai/Nippon Thompson Co. Ltd. 9/8/87 4,692,036 Kawaguchi/Nippon Thompson Co. 8/25/87 4,688,950 Yokota/Nippon Thompson Co. 8/18/87 4,687,345 Geka/Nippon Thompson Co. 4/21/87 4,659,238 Teramachi 1/7/86 4,563,045 Katayama 4/16/85 4,511,189 Mottate/Nippon Thompson Co. 1/29/85 4,496,197 Kwon/Bendix Corporation 8/2/83 4,396,235 Teramachi ______________________________________
SUMMARY OF THE INVENTION
With the above in mind it is the object of this invention to provide an elegant parallel roller type bearing which is easy to manufacture, has reasonable cost, and overcomes the aforenoted prior art defects.
As will be described in detail the invention features the provision of a roller bearing device of the parallel type, which in the preferred embodiment, has an endless roller groove which is constructed solely in the first member (car) in a manner which retains the rollers therein without need of caps/end plates/etc., the second member (track) together with the endless groove in the first member being the sole retention means for trappingly retaining the rollers therebetween.
Another feature of the invention is to provide a parallel roller device wherein the end surfaces of the rollers provide sliding movement and the curved surface provides rolling movement of the rollers to afford burdening of the rollers on the relatively moving members from all four load quadrants.
Another aspect is to provide an endless parallel roller type device wherein the end surfaces of each of a plurality of rollers may slidingly engage both the base of the endless U-shaped groove in one member and the opposed flat surface of the other member when the load is generally parallel to the axis of the rolling surfaces when no interposed restraint is employed, or if employed is disengaged.
The features of the invention may be further characterized as providing high lubricity surfaces for the potential sliding engagement of the end surfaces of the roller on the relatively moving members.
Another aspect is to have rollers made of softer material compared to the other two movable members of a parallel roller bearing assembly such that when debris is unavoidably trapped on the load bearing surfaces, the damage will be to the rollers rather than the rolled upon surfaces of the more costly track and car members of the assembly.
The invention features a construction wherein a pair of "relaxed rubber band shaped" grooves which are U-shaped in cross section are formed in a car for presenting a plurality of rollers into engagement with a pair of spaced right angled working portions of a track, one part of each of the right angled portions of the track being operative to receive a sliding end surface of a plurality of rollers and a second part of each of the right angled portions of the track being operative to receive rolling engagement of the rolling surface of the rollers.
Another feature of the invention is to provide a bearing apparatus having a track with a shape approximating an X shape in cross section to provide 4 bearing track surfaces, wherein the car associated with the X shaped track has a pair of endless U-shaped grooves, one such U-shaped groove being formed in each of opposite sides of a vertical center line through said X shaped track for presenting parallel rollers located therein respectively into operative relationship with each of the two angularly disposed surfaces of the track on each respective side of the vertical center line to provide a bearing of great simplicity and few parts.
Another object is to utilize a bearing of the type above discussed in relatively high precision apparatus for X axis and/or Y axis and/or Z axis devices to provide relatively high precision movement in any of or all three planed at low cost, quite low mass and relatively high precision.
Another feature is to provide a corrosion resistant and relatively high load bearing device which is easy to maintain and is well adapted for use on sailboats where humans may come into contact therewith.
Another aspect of the invention is a construction wherein both the car and the track member may be formed from extruded aluminum, which after formation of the grooves in the car, is surface coated with a high lubricity hard coat which affords easy sliding relative movement of the end surfaces of the rollers with both the track and the car, corrosion resistance of both car and track and high density wear surfaces.
Still another aspect of the invention is to provide a construction in an alternate form of bearing having many of the above characteristics wherein the track member may be roll formed with a resulting reasonably high degree of precision.
Another feature is a construction which may provide a track useful in a parallel roller devices described above wherein, in some embodiments, an extruded central elongated chamber may be formed which is well adapted to cooperate with a piston which, when operated by air pressure, etc., can move the car and track relative to each other on the parallel rollers.
Another aspect of the invention is to provide the aforementioned track chamber which is operative to surround a screw of a ball screw mechanism or a rack of a rack and pinion mechanism and thereby keep such moving parts clean from contaminant, dirt or debris which may affect precision of their movement.
A further feature is to provide a simple up down Z tower utilizing the bearing mechanism and features aforementioned which is low in cost, high in reliability and considerably lower in weight than prior devices without sacrifice of required precision of relative movement.
Another aspect of the invention is to provide a device wherein the endless grooves for receipt of the parallel rollers are geometrically arranged in the car for "single set up" machining and no machining is required for the track roller engaging working surfaces.
Another object is to provide an alternate device wherein the car may be a four groove car operating from a single side (180 degrees) only of a rail track wherein an additional element, namely a combination cover/attachment means, retains the rollers in two of the four grooves, permitting roller surface engagement type operations when loaded from any of the four quadrants while still requiring only a single car means and track means construction, there being roller loaded and non loaded versions.
Another overall feature of the inventive concepts is to provide roller bearing devices of wide versatility of uses which requires a relatively low inventory of parts.